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COMP 3322B Modern Technologies on World Wide WebInternet Basics (O1)Dr. C Wu Department of Computer Science The University of Hong Kong2nd semester 2018-2019
What is the Internet? A global system of interconnected computer networks linking billions of devices throughout the worldhosts == end systems, running network applicationsrouters and switchescommunication linksTwisted paircopper wireFiber op)cscoaxial cablee.g. desktop PC, server, laptop, smartphone, tabletse.g. Web, email, ftp, BitTorrent, Skype,...switching devices that end systems are directly connected to forward data from one host to anothermobile network global ISP regional ISP home network institutional network smartphone PC server wireless laptop wired links wireless links router
What is the Internet? A network of networks interconnected ISPs A communication infrastructure to support network applications end systems and routers run protocolsto send and receive data to/from each othermobile network global ISP regional ISP home network institutional network smartphone PC server wireless laptop wired links wireless links router
Network protocolA human protocolHiHiWhat’sthe+me?5pmA network protocol defines format, order of msgs sent and received between network entities actions taken on msg transmission/receiptWeb browserWeb serverConnectrequestConnectreplyGETindex.html<filecontent>
Internet protocol stackThere are 5 layers in the Internet protocol suite Each layer performs certain actions within that layer uses the service provided by the layer directly below it Each layer implements different protocolsPhysical layerLink layerNetwork layerTransport layerApplica6on layerNetwork protocols are organized in layers
Internet protocol stack Physical layerLink layerNetwork layerTransport layerApplica6on layerPhysical layerLink layerNetwork layerTransport layerApplica6on layerLink layerPhysical layerLink layerPhysical layerNetwork layersource hostdes+na+on hostswitchrouterWeb browserWeb serverresponsible for retrieving, presen0ng and transmi4nginforma0on(HTTP, DNS, etc.)responsible for delivering data between twoapplica+on programson two hosts(TCP, UDP)responsible for delivering data between twohosts(IP,rou0ng protocols)responsible for delivering data between two adjacentnetwork elements(Ethernet, WiFi, etc.)Different devices implement different numbers of layersresponsible for delivering individual bits on thecommunica+on link